This invention relates to 8-halo-6-nitro-1,2,4-triazolo[4,3-a]pyrazine 5-amine compounds and the acid addition salts thereof, used to selectively sensitize tumor cells to therapeutic radiation and thus increase the effective therapeutic ratio of radiologic treatment. In addition, the present invention relates to pharmaceutical compositions comprising such pyrazine compounds and to methods of treatment comprising administering such compounds to patients undergoing radiation therapy to enhance the effectiveness of such treatment.
At the present time, certain other unrelated compounds are in experimental clinical use as radiation sensitizers. However, these compounds--for example, metronidazole and misonidazole--suffer from the drawback that they also cause symptoms of neurotoxicity which limits their usefulness. The compounds of the present invention are effective radiation sensitizers, but are believed to have a more favorable therapeutic ratio.